Hydraulic conductivity of conifer sapwood varies greatly between and within annual rings due to varying dimensions and numbers of tracheids, lumina and bordered pits, complex relationships and non-linearities. Existing laboratory methods are too tedious and expensive for large scale studies for instance of genetics, tree improvement and silvicultural practices, and their spatial resolution is not enough for information on seasonal weather effects which may reflect vulnerability to drought. The article presents a set of integrated models estimating radial variations in hydraulic conductivity at the tracheid level, at 25 µm resolution. A rationalised model was designed for the organisation of tracheids and the water transport through lumina and bordered pits. Within this, pressure drops at flow along lumina and at passages of pits are estimated and integrated to provide local estimates of lumen and xylem conductivities with same radial resolution. The estimated lumen conductivities varied from maximum 0.030 m2/(s·MPa) in earlywood to minimum 0.001 m2/(s·MPa) in latewood. Estimated pressure drops on pit passages reduce these values with about 80 and 90 % into xylem conductivities of 0.006 and 0.0001 m2/(s·MPa) in same earlywood and latewood. Sample means of modelled trunk xylem conductivities were correlated with data from laboratory analyses, resulting in R2 > 0.50.
The European Commission is acknowledged for its funding of the project “Designing Trees for the Future”, T4F, 2011–2016, which became the starting point of this research effort.